Rubber mixtures for producing highly reinforced vulcanisates with low damping behaviour

ABSTRACT

The rubber mixtures according to the invention consisting of a rubber, a filler and a specific sulphurized mineral oil are suitable for producing shaped vulcanizates, in particular for producing tires with reduced rolling resistance and high resistance to wet skidding, and tires with particularly reinforced side walls (“run flat tires”).

[0001] The present patent application relates to rubber mixturesconsisting of rubber, filler and a specific sulphurised mineral oil.Vulcanisates with surprisingly good reinforcement- andtemperature-dependent dynamic damping behaviour which are particularlysuitable for producing tires with low-damping treads with a highresistance to wet skidding and for producing tires with low-dampinghighly reinforced lateral walls can be produced from the rubber mixturesaccording to the invention.

[0002] Mineral oils are often added to rubbers and rubber mixtures toimprove the processing properties. The differing content of paraffinic,naphthenic and aromatic contents in the mineral oils is known to have acorresponding effect on the damping properties of the rubbervulcanisates produced, wherein, disadvantageously, it is not possible toimprove both the rolling resistance and the resistance to wet skiddingtogether in tires by altering the mineral oil composition, but only oneof the two properties at the cost of the other. In this regard, seeKautschuk, Gummi, Kunststoffe 44, 1991, page 528 to 536.

[0003] Therefore, it was an object of the present invention to providerubber mixtures containing a specific mineral oil which do not havethese disadvantages in the damping behaviour of the vulcanisates.

[0004] Many methods of producing vehicle tires with low-damping tiretreads and low-damping highly reinforced lateral walls have beeninvestigated. U.S. Pat. No. 5,227,425 thus describes the production oftire treads with low rolling resistance and with high resistance to wetskidding made of solution SBR rubber, silica, conventional aromaticmineral oil and a polysulphide-containing silyl ether. The mineral oilcertainly improves the flowability and processibility of the rubbermixtures, but simultaneously reduces the reinforcement level. To obtainacceptable reinforcement properties, large quantities of an expensivepolysulphide-containing silyl ether are therefore required.

[0005] Therefore, a further object of the present invention was toprovide mineral oil-containing rubber mixtures and vulcanisates withimproved reinforcement behaviour.

[0006] JP-B 47 008 135 describes reaction products of aromatic mineraloils with sulphur monochloride for improving the processing behaviour ofrubber mixtures. The modified mineral oils are produced by a methodwhich predominantly leads to mono- and disulphide bridges due to thechemical nature of sulphur monochloride. Moreover, the sulphurmonochloride used leads to an undesirable residue of bound chlorine inthe end product.

[0007] It has now been found that rubber vulcanisates with exceptionallyfavourable dynamic damping behaviour and an exceptionally highreinforcement level can be obtained from rubber mixtures containingcertain sulphurised mineral oils and that rubber mixtures of this typeare suitable, in particular, for producing tires which are resistant towet skidding with particularly low rolling resistance and for producingtires with low damping with highly reinforced lateral walls (“run flattires”).

[0008] The present invention therefore relates to rubber mixturesconsisting of a rubber, a fillet and optionally further rubberauxiliaries and cross-linking agents and 0.1 to 75 parts by weight,based on 100 parts by weight of rubber, of a specific sulphurisedmineral oil, the sulphurised mineral oil having been obtained byreacting an aromatic-containing mineral oil with sulphur.

[0009] The sulphurised mineral oil used was produced according to theinvention in that an aromatic-containing mineral oil with an aromaticcontent according to ASTM D 2140 of 5 to 50 wt. % and aviscosity-density constant VDK of 0.82 to 1.05 was reacted with 2.5 to40 parts by weight of sulphur per 100 parts by weight of mineral oil attemperatures of 130 to 250° C., optionally in the presence of catalysts.

[0010] The sulphurised mineral oils according to the invention have abound sulphur content of 2.5 to 12.5 wt. %, preferably 4 to 10 wt. %,and a glass transition temperature (determined by DSC) of −25 to −65°C., preferably −35 to −55° C., and a density of 0.85 to 1.1 g/cm³,preferably 0.92 to 1.03 g/cm³ (at 20° C.).

[0011] The viscosities are 0.3 to 100 Pa.sec, particularly preferably0.8 to 20 Pa.sec at 20° C. (plate and cone viscometer, 20 rpm).

[0012] The starting products for producing the sulphurised mineral oilsused according to the invention are aromatic-containing mineral oilswith an aromatic content (according to ASTM D 2140) of 5 to 50%,preferably 15 to 40%, a viscosity-density constant VDK (according toASTM D 2501) of 0.82 to 1.05, preferably 0.84 to 1.0. Preferredaromatic-containing mineral oils moreover have a density of 0.85 to 1.03g/cm³ (at 15° C.), preferably 0.9 to 1.0 g/cm³ and a pour point(according to ASTM D 97) between −20° C. and +30° C., particularlypreferably between −15° C. and +20° C., and contain less than 0.1 wt. %,preferably less than 0.005 wt. %, of polycyclic aromatic hydrocarbonsand/or a DMSO-extract according to IP 346<3 wt. %. Mineral oil productsof this type are commercially available; suitable products are, forexample, Enerthene® 1849-1 (BP) and Catenex Oil SNR® (Shell). In thisregard see Kautschuk, Gummi, Kunststoffe, 45 (1992), pages 24-29.

[0013] The reaction of aromatic-containing mineral oils with sulphur ispreferably carried out with 5 to 20 parts by weight of sulphur per 100parts by weight of aromatic-containing mineral oils at temperatures ofpreferably 160 to 220° C., particularly preferably 180 to 210° C., for atime period of a few minutes (5 min) up to several hours (10 hours),optionally in the presence of catalysts. Suitable catalysts are acidicor basic catalysts, such as zinc chloride, aluminium chloride, tinchloride, hydrogen sulphide and/or alkyl amines, such as dodecylamine oroctadecylamine. Suitable quantities of catalysts are 0.01 to 3 parts byweight based on aromatic-containing mineral oil. However, the reactionis preferably carried out without a catalyst.

[0014] Following the reaction, residues of hydrogen sulphide andvolatile mercaptans can be removed, for example, by applying a vacuum orblowing out with nitrogen or by chemical methods, such as oxidisingagents (for example atmospheric oxygen or peroxides). Unreacted sulphurcan be removed by filtering off, for example.

[0015] In addition to natural rubbers, synthetic rubbers are alsosuitable for producing the rubber mixtures and vulcanisates according tothe invention. Preferred synthetic rubbers are described, for example,in W. Hofmann, Kautschuktechnologie, Gentner Verlag, Stuttgart 1980 andI. Franta, Elastomers and Rubber Coumpounding Materials, Elsevier,Amsterdam 1989. They include inter alia

[0016] BR—polybutadiene

[0017] ABR—butadiene acrylic acid-C1-4-alkyl ester copolymers

[0018] CR—polychloroprene

[0019] IR—polyisoprene

[0020] SBR—styrene/butadiene copolymers with styrene contents of 1-60,preferably 20-50 wt. %

[0021] IIR—isobutylene isoprene copolymers

[0022] NBR—butadiene acrylonitrile copolymers with acrylonitrilecontents of 5-60, preferably 10-40 wt. %

[0023] HNBR—partially or completely hydrogenated NBR rubber

[0024] EPDM—ethylene propylene diene copolymers

[0025] and mixtures of these rubbers. Of interest for the production ofcar tires, are, in particular, natural rubber, emulsion SBR and solutionSBR rubbers with a glass transition temperature above −50° C. which canoptionally be modified with silyl ethers or other functional groupsaccording to EP-A 447 066, polybutadiene rubber with a high1.4-cis-content (>90%) produced by catalysts based on Ni, Co, Ti or Nd,and polybutadiene rubber with a vinyl content of up to 75% and mixturesthereof. Most particularly preferred are the so-called solution SBR andpolybutadiene rubbers.

[0026] The rubber mixtures according to the invention contain thefillers known and used in the rubber industry; these include both theactive and the inactive fillers, notably:

[0027] fine-particled silicas, produced, for example, by precipitationof solutions of silicates or flame hydrolysis of silicon halides withspecific surface areas of 5 -1000, preferably 20-400 m²/g (BET surfacearea) and with primary particle sizes of 10-400 nm. The silicas canoptionally be present as mixed oxides with other metal oxides, such asAl, Mg, Ca, Ba, Zn, Zr, Ti oxides;

[0028] synthetic silicates, such as aluminium silicate, alkaline-earthsilicate such as magnesium silicate or calcium silicate, with BETsurface areas of 20-400 m²/g and primary particle diameters of 10-400nm;

[0029] natural silicates such as kaolin and other naturally occurringsilicas;

[0030] glass-fibres and glass-fibre products (mats, strands) or glassmicrobeads;

[0031] metal oxides, such as zinc oxide, calcium oxide, magnesium oxide,aluminium oxide;

[0032] metal carbonates, such as magnesium carbonate, calcium carbonate,zinc carbonate;

[0033] metal hydroxides, such as for example, aluminium hydroxide,magnesium hydroxide;

[0034] carbon blacks. The carbon blacks to be used in this process areproduced by the lamp black, furnace or gas black process and have BETsurface areas of 20-200 m²/g, for example, SAF, ISAF, HAF, FEF or GPFcarbon blacks;

[0035] rubber gels

[0036] rubber powder, obtained, for example, by size-reduction of rubbervulcanisates. Preferred particle sizes are between 0.001 to 0.5 mm.

[0037] Fine-particle silicas and carbon blacks, optionally together withrubber powder, are preferably used as fillers.

[0038] The fillers mentioned can be used alone or in a mix, specificallyin quantities of 1 to 300 parts by weight, preferably 10 to 150 parts byweight based on 100 parts by weight of rubber. In a particularlypreferred embodiment, the rubber mixtures contain as fillers, a mixtureof light fillers, such as fine-particled silicas, and carbon blacks, themixing ratio of light filler to carbon blacks being 1:0.05 to 20,preferably 1:0.1 to 10.

[0039] The rubber mixtures according to the invention can obviously alsocontain other rubber auxiliaries and cross-linking agents. Sulphur orsulphur-supplying compounds or peroxides are used as cross-linkingagents. Particularly preferred are sulphur or sulphur-supplyingcompounds in quantities of 0.01 to 3 parts by weight based on rubber.

[0040] Furthermore, as mentioned, the rubber mixtures according to theinvention can contain further auxiliary agents, such as the knownreaction accelerators, anti-ageing agents, heat stabilisers, lightprotection agents, ozone protection agents, process aids, reinforcingresins, for example phenolic resins, steel cord bonding agents, such as,for example, silica/resorcinol/hexamethylenetetramine orcobalt-naphthenate, plasticisers, tackifiers, blowing agents, dyes,pigments, waxes, extenders, organic acids, retarding agents, metaloxides and activators.

[0041] The rubber auxiliaries are used in the usual, known quantities,the quantity used depending on the subsequent intended purpose of therubber mixtures. For example, normal quantities of rubber auxiliariesare in the range of 2 to 70 parts by weight, based on 100 parts byweight of rubber.

[0042] The use of additional filler activators is particularlyadvantageous for the rubber mixtures according to the invention whichare filled with highly active silicas. Preferred filler activators aresulphur-containing silyl ethers, in particularbis-(trialkoxysilyl-alkyl)-polysulphides as described in DE-A 2 141 159and DE-A 2 255 577. Further possibilities are oligomeric and/orpolymeric sulphur-containing silyl ethers according to the descriptionin DE-A 4 435 311 and EP-A 670 347. Mercapto-alkyltrialkoxysilanes, inparticular mercaptopropyltriethoxysilane and thiocyanatoalkylsilylethers(see DE-A 19 544 469), amino group-containing silyl ethers, such as forexample 3-amino-propyltriethoxysilane andN-oleyl-N-propyl-trimethoxysilane and trimethylolpropane. The filleractivators are used in the usual quantities, i.e. in quantities of 0.1to 15 parts by weight, based on 100 parts by weight of rubber.

[0043] The rubber mixtures according to the invention can be produced,for example, by mixing the rubbers with the fillers, rubber auxiliariesand the sulphurised mineral oils in suitable mixing apparatuses, such askneaders, rollers or extruders, or by mixing the rubber solutions withfillers and the sulphurised mineral oils and removing the solvent, forexample by steam distillation.

[0044] The present invention also relates to the use of the rubbermixtures according to the invention for producing vulcanisates which, inturn, are used for the production of highly reinforced rubber shapedarticles, in particular for the production of tires.

[0045] Particularly preferred is the use of the rubber mixtures forproducing tire treads with low rolling resistance and resistance to wetskidding and for producing particularly reinforced lateral walls fortires with emergency running properties (“run flat tires”), asdescribed, for example, in U.S. Pat. No. 5,368,082, EP-A 475 258, U.S.Pat. No. 5,427,166, U.S. Pat. No. 5,511,599 and EP-A 943 466.

EXAMPLES Example 1 Sulphurised Mineral Oil with 5.3 wt. % of BoundSulphur

[0046] 100 g sulphur were added to 1,000 g Enerthene 1849-1(solvent-refined mineral oil from BP, aromatics content according toASTM D 2140: 24%, density 0.945 g/cm³, S content 0.9%, pour point 0° C.,VDK 0.884, polycyclic aromatic compound content <50 ppm), DMSO-extract(according to IP 346): 2.2 wt.%) and heated for 2 hours to 200° C.,hydrogen sulphide being released. A vacuum was then applied for 10minutes at 110° C. to remove the released hydrogen sulphide. 1,045 g ofa black oil were obtained with a sulphur content of 5.3 wt.%, viscosity5 Pa.sec (plate and cone, 20 rpm, 20° C.), glass transition temperatureof −50° C. (according to DSC) and density 0.97g/cm³.

Example 2 Rubber Mixtures and Vulcanisates

[0047] The following rubber mixtures were produced in a 1.51 kneader.(Mixing time: 5 minutes, speed 60 rpm). The sulphur and acceleratorswere finally added on a roller at 50° C.: Comparison Example Example 2.12.A 2.B Mixed in the kneader: L-SBR Buna VSL 5025-0 (Bayer AG) 70 70 70Polybutadiene Buna CB 25 30 30 30 (Bayer AG) Silica Vulkasil 5 70 70 70(Bayer AG) Aromatic mineral oil Enerthene 1849-1 (BP) 37.5 17.5 0Sulphurised mineral oil, 0 20 37.5 Example 1 Zinc oxide 2.5 2.5 2.5Stearic acid 1 1 1 Antioxidant Vulkanox 4020 (Bayer AG) 1 1 1 Silane Si69 (Degussa Hüls) 5.6 5.6 5.6 Mixed on the roller: Sulphur 1.5 1.5 1.5Accelerator Vulkacit CZ 1.8 1.8 1.8 (Bayer AG) Accelerator Vulkacit D 22 2 (Bayer AG) Mooney-Viscosity ML 1 + 4 41 43 45 (100° C.)

[0048] The mixtures were then vulcanised for 15 minutes at 170° C. Thefollowing vulcanisate properties were found: Comparison Example Example2.1 2.A 2.B Tensile modulus 100% 2.2 2.8 3.3 elongation (MPa) Tensilemodulus 300% 8.4 10.8 12.5 elongation (MPa) Tensile strength (MPa) 15.716.1 17 Rebound at 23° C. (%) 34 33 32 Rebound at 70° C. (%) 53 59 60Shore A hardness (23° C.) 60 63 66 Abrasion DIN 53.516 (mm³) 109 92 93

[0049] The test results show that vulcanisates with improved dynamicdamping properties (low rebound at 23° C. correlated with highresistance to wet skidding in tires, high rebound at 70° C. correlatedwith low rolling resistance in tires) and low abrasion at asignificantly higher reinforcement level can be produced from the rubbermixtures with the content according to the invention of sulphurisedmineral oils (I).

1. Rubber mixtures consisting of a rubber, a filler and 0.1 to 75 partsby weight, based on 100 parts by weight of rubber, of a sulphurisedmineral oil, wherein the sulphurised mineral oil is obtained by reactingan aromatic-containing mineral oil with sulphur.
 2. Rubber mixturesaccording to claim 1, characterised in that the sulphurised mineral oilhas a bound sulphur content of 2.5 to 12.5 wt. %, a glass transitiontemperature of −25 to −65° C. and a density of 0.85 to 1.1 g/cm³.
 3. Useof the rubber mixtures according to the invention and according to claim1 for producing shaped vulcanisates, in particular for producing tireswith reduced rolling resistance and high resistance to wet skidding andtires with particularly reinforced lateral walls (“run flat tires”).